Access stratum manager

ABSTRACT

A multi-mode mobile communication device may include a processing device, a memory sub-system, a communication sub-system operable to communicate with the plurality of wireless access networks, and a protocol stack stored in the memory sub-system and executed by the processing device. The protocol stack may include a first access stratum, a second access stratum, a non-access stratum and an access stratum manager. The first access stratum may communicate with a first wireless access network via the communication sub-system. The second access stratum may communicate with a second wireless access network via the communication sub-system. The non-access stratum may communicate with a core network. The access stratum manager may interface the non-access stratum with the first and second access strata, and may be operable to activate the first access stratum to establish a communication link with the core network over the first wireless access network. The access stratum manager may be further operable to maintain the communication link between the non-access stratum and the core network while transferring the communication link from the first access stratum to the second access stratum.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from and is related to the followingprior applications: “Radio Access Technology Manager,” U.S. ProvisionalApplication No. 60/416,154, filed Oct. 4, 2002; and “Radio AccessTechnology Manager,” U.S. Provisional Application No. 60/416,864, filedOct. 8, 2002. These prior applications, including the entire writtendescriptions and drawing figures, are hereby incorporated into thepresent application by reference.

FIELD

The technology described in this patent document relates generally tothe field of mobile communication systems. More particularly, the patentdocument describes an access stratum manager for use in a mobilecommunication device.

BACKGROUND

UMTS (Universal Mobile Telecommunications System) is a third generationpublic land mobile telecommunication system. Various standardizationbodies publish standards for UMTS, each in their respective areas ofcompetence. For instance, the 3GPP (Third Generation PartnershipProject) publishes standards for GSM (Global System for MobileCommunications) and W-CDMA (Wideband Code Division Multiple Access)based UMTS, and the 3GPP2 (Third Generation Partnership Project 2)publishes standards for CDMA2000 (Code Division Multiple Access) basedUMTS. Standard document 3GPP TS 22.129 addresses UMTS handoverrequirements between UTRAN (UMTS Terrestrial Access Network) and otherradio systems, and is incorporated herein by reference.

SUMMARY

A multi-mode mobile communication device may include a processingdevice, a memory sub-system, a communication sub-system operable tocommunicate with the plurality of wireless access networks, and aprotocol stack stored in the memory sub-system and executed by theprocessing device. The protocol stack may include a first accessstratum, a second access stratum, a non-access stratum and an accessstratum manager. The first access stratum may communicate with a firstwireless access network via the communication sub-system. The secondaccess stratum may communicate with a second wireless access network viathe communication sub-system. The non-access stratum may communicatewith a core network. The access stratum manager may interface thenon-access stratum with the first and second access strata, and may beoperable to activate the first access stratum to establish acommunication link with the core network over the first wireless accessnetwork. The access stratum manager may be further operable to maintainthe communication link between the non-access stratum and the corenetwork while transferring control of the communication link from thefirst access stratum to the second access stratum. The multi-mode mobilecommunication device may measure the respective signal strengths of thefirst wireless access network and the second wireless access network,and the access stratum manager may initiate the transfer of control ofthe communication link from the first access stratum to the secondaccess stratum in response to a handover control signal generated byfirst access stratum in response to the measured signal strengths.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example multi-mode access network(MMAN);

FIG. 2 is a block diagram illustrating a typical UTRAN;

FIG. 3 is a block diagram of a typical core network;

FIG. 4 is a block diagram illustrating an example mobile communicationdevice;

FIG. 5 is a block diagram of an example multi-mode mobile communicationdevice;

FIG. 6 is a block diagram of an example dual-mode protocol stack for amulti-mode mobile communication device;

FIG. 7 is a more-detailed block diagram of the example dual-modeprotocol stack shown in FIG. 6 that illustrates example sub-programs forinitiating and controlling the handover procedure between the UMTS andGSM access networks; and

FIGS. 8-15 are signal flow diagrams illustrating example operations of adual mode protocol stack.

DETAILED DESCRIPTION

With reference now to the drawing figures, FIG. 1 is a block diagram ofan example multi-mode access network (MMAN) 100. The MMAN 100 includesmultiple zones 5, 25, 55, 65 and 75, within which a multi-mode mobilecommunication device 10 may communicate with multiple access networks20, 30, 40, 50 and 60. The zones may include a personal zone 5, a picozone 25, a micro zone 55, a macro zone 65, and a global zone 75. Theaccess networks may include a plurality of personal access networks(PAN1-PANp) 20, a plurality of broadband radio access networks(BRAN1-BRANb) 30, a plurality of UTRANs (UTRAN1-UTRANu) 40, a pluralityof GSM EDGE (Enhanced Data-rates for Global Evolution) Radio AccessNetworks (GERAN1-GERANg), and a plurality of satellite networks(Satellite 1-Satellite s). Also illustrated is a core network 70, whichmay be accessed by the multi-mode mobile communication device 10 via theMMAN 100. It should be understood that the zones 5, 25, 55, 65 and 75illustrated in FIG. 1 are scaled relative to one another to show thataccess networks in a particular zone, such as the plurality of UTRANs 40and GERANs 50, may provide network access to the multi-mode mobilecommunication device 10 within any zone smaller than the macro zone 65.

The personal access networks (PAN1-PANp) 20 may, for example, includeshort-range communication networks, such as BlueTooth™, infrared, or awired access network, such as a local area network (LAN). The broadbandradio access networks (BRAN1-BRANb) 30 may utilize medium-rangecommunications, such as IEEE 802.11 communication systems.

The multi-mode mobile communication device 10 is operable to handovercommunications from one access network to another. That is, when themulti-mode mobile communication device 10 moves within a zone or fromone zone to an adjacent zone, the multi-mode mobile communication device10 may change mode to access alternate networks. For example, as themulti-mode mobile communication device 10 moves from a rural area inglobal zone 75, moves through a sub-urban area in a macro-zone 65, movesthrough a more densely populated urban area in micro-zone 55, enters abuilding in pico zone 25, and finally enters an office in personal zone5, the multi-mode mobile communication device 10 attempts to accessmultiple networks using different modes, such as satellites 60, GERANs50 and UTRANs 40, BRANs 30 and PANs 20, respectively. A more-detaileddescription of the multi-mode mobile communication device 10 is providedbelow.

FIG. 2 is a block diagram illustrating a typical UTRAN 240. Alsoillustrated is a multi-mode mobile communication device 210 thatcommunicates with a core network 270 via the UTRAN 240. The UTRAN 240includes multiple Node B's 215, of which only two are illustrated, tocommunicate wirelessly using radio waves over the Uu interface with themulti-mode mobile communication device 210. Depending on thecapabilities of a particular UTRAN 240, an RNC 230 may support multipleNode B's of the same mode or multiple Node B's operating in diversemodes. An ATM (Asynchronous Transfer Mode) backbone 220 couples thevarious UTRAN 240 components together, and couples the UTRAN 240 to thecore network 270.

FIG. 3 is a block diagram of a typical core network 370. Alsoillustrated is a multi-mode mobile communication device 310, whichco-operates with one or more access networks 340 to communicate with theUMTS core network 370 via an ATM backbone 320. In operation, circuitswitched (CS) packets may be sent and received via a transcoder/rateadapter unit (TRAU) 310, which converts UMTS speech packets to standardpackets for a mobile switching center (MSC) 330 in order to communicatespeech over a public switched telephone network (PSTN) 350. In addition,packet switched (PS) packets may be sent and received via a serving GPRS(General Packet Radio Service) support node (SGSN) 360, private IPbackbone 380, Gateway GPRS Support Node (GGSN) 390, and external packetnetwork 395.

Also included in the core network 370 are a visitor location register(VLR) 365 and a home location register/authentication center (HLR/AuC)355. The VLR 365 stores the multi-mode mobile communication device 310information required for call handling and other functions within anassociated service area. The HLR/AuC 355 stores permanent records usedto identify the multi-mode mobile communication device 310, and may alsostore temporary records, such as SGSN and VLR addresses.

FIG. 4 is a block diagram illustrating an example mobile communicationdevice 400. The mobile communication device 400 includes a processingdevice 438, a communications subsystem 411, a short-range communicationssubsystem 440, input/output devices 422, 428, 430, 432, 434, 436, memorydevices 424, 426, and various other device subsystems 442. The mobilecommunication device 400 is preferably a two-way communication devicehaving voice and data communication capabilities. In addition, thedevice 400 preferably has the capability to communicate with othercomputer systems via the Internet.

The processing device 438 controls the overall operation of the mobilecommunication device 400. Operating system software executed by theprocessing device 438 is preferably stored in a persistent store, suchas a flash memory 424, but may also be stored in other types of memorydevices, such as a read only memory (ROM) or similar storage element. Inaddition, system software, specific device applications, or partsthereof, may be temporarily loaded into a volatile store, such as arandom access memory (RAM) 426. Communication signals received by themobile communication device 400 may also be stored to RAM 426.

The processing device 438, in addition to its operating systemfunctions, enables execution of software applications 458, 450, 452,454, 456 on the device 400. A predetermined set of applications thatcontrol basic device operations, such as data and voice communications,may be installed on the device 400 during manufacture. In addition, apersonal information manager (PIM) application may be installed duringmanufacture. The PIM is preferably capable of organizing and managingdata items, such as e-mail, calendar events, voice mails, appointments,and task items. The PIM application is also preferably capable ofsending and receiving data items via a wireless network 419. Preferably,the PIM data items are seamlessly integrated, synchronized and updatedvia the wireless network 419 with the device user's corresponding dataitems stored or associated with a host computer system.

Communication functions, including data and voice communications, areperformed through the communication subsystem 411, and possibly throughthe short-range communications subsystem 440. The communicationsubsystem 411 includes a receiver 412, a transmitter 414 and one or moreantennas 416, 418. In addition, the communication subsystem 411 alsoincludes a processing module, such as a digital signal processor (DSP)420 or other processing device(s), and local oscillators (LOs) 413. Thespecific design and implementation of the communication subsystem 411 isdependent upon the communication network in which the mobilecommunication device 400 is intended to operate. For example, a mobilecommunication device 400 may include a communication subsystem 411designed to operate within the Mobitex™ mobile communication system, theDataTAC™ mobile communication system, a GSM network, a GPRS network, aUMTS network, and/or an EDGE network.

Network access requirements vary depending upon the type ofcommunication system. For example, in the Mobitex and DataTAC networks,mobile communication devices are registered on the network using aunique personal identification number or PIN associated with eachdevice. In UMTS and GSM/GPRS networks, however, network access isassociated with a subscriber or user of a device. A GPRS devicetherefore requires a subscriber identity module, commonly referred to asa SIM card, in order to operate on a GSM/GPRS network.

When required network registration or activation procedures have beencompleted, the mobile communication device 400 may send and receivecommunication signals over the communication network 419. Signalsreceived by the antenna 416 from the communication network 419 arerouted to the receiver 412, which provides for signal amplification,frequency down conversion, filtering, channel selection, etc., and mayalso provide analog to digital conversion. Analog-to-digital conversionof the received signal allows the DSP to perform more complexcommunication functions, such as demodulation and decoding. In a similarmanner, signals to be transmitted to the network 419 are processed(e.g., modulated and encoded) by the DSP 420 and are then provided tothe transmitter 414 for digital to analog conversion, frequency upconversion, filtering, amplification and transmission to thecommunication network 419 (or networks) via the antenna 418.

In addition to processing communication signals, the DSP 420 providesfor receiver 412 and transmitter 414 control. For example, gains appliedto communication signals in the receiver 412 and transmitter 414 may beadaptively controlled through automatic gain control algorithmsimplemented in the DSP 420.

In a data communication mode, a received signal, such as a text messageor web page download, is processed by the communication subsystem 411and input to the processing device 438. The received signal is thenfurther processed by the processing device 438 for output to a display422, or alternatively to some other auxiliary I/O device 428. A deviceuser may also compose data items, such as e-mail messages, using akeyboard 438 and/or some other auxiliary I/O device 428, such as atouchpad, a rocker switch, a thumb-wheel, or some other type of inputdevice. The composed data items may then be transmitted over thecommunication network 419 via the communication subsystem 411.

In a voice communication mode, overall operation of the device issubstantially similar to the data communication mode, except thatreceived signals are output to a speaker 434, and signals fortransmission are generated by a microphone 436. Alternative voice oraudio I/O subsystems, such as a voice message recording subsystem, mayalso be implemented on the device 400. In addition, the display 422 mayalso be utilized in voice communication mode, for example to display theidentity of a calling party, the duration of a voice call, or othervoice call related information.

The short-range communications subsystem 440 enables communicationbetween the mobile communication device 400 and other proximate systemsor devices, which need not necessarily be similar devices. For example,the short-range communications subsystem 440 may include an infrareddevice and associated circuits and components, or a Bluetooth™communication module to provide for communication with similarly-enabledsystems and devices.

In addition, if the mobile communication device is a multi-mode mobilecommunication device, as described herein, then protocol stacks 446,including an access stratum manager, may be included. The multi-modeprotocol stacks and the access stratum manager are described in moredetail below.

FIG. 5 is a block diagram of an example multi-mode mobile communicationdevice 1000. The device 1000 includes a plurality of device applications1002, 1004, 1006, a non-access stratum (NAS) module 1008, an accessstratum manager (ASM) module 1010, a UMTS access module 1012, and a GSMaccess module 1014. Also illustrated are a UMTS access network 1018, aGSM access network 1020, and a core network 1024.

The device applications may include an IP application 1002 (e.g., anelectronic mail application, a web browser application, or others), atelephony application 1004, and/or other applications 1006 thatcommunicate with the core network 1024. The device applications 1002,1004, 1006 may, for example, be software applications stored in a memorysub-system and executed by a processing sub-system. For example, withreference to FIG. 4, the device applications may be stored in the flashmemory 424 and/or RAM 426 and executed by the microprocessor 438 and/orDSP 420. The NAS module 1008, ASM module 1010, UMTS access module 1012,and GSM access module 1014 may be software, hardware, or a combinationof software and hardware for implementing a dual-mode protocol stackthat is used to setup and maintain communications between the deviceapplications 1002, 1004, 1006 and the core network 1024 over one of theaccess networks 1018, 1020.

The NAS module 1008 includes the non-access stratum software and anyassociated hardware for communicating with the core network 1024. TheNAS module 1008 applies the wireless protocols necessary to interfacethe application layers 1002, 1004, 1006 with the core network 1024.

The UMTS module 1012 includes the UMTS access stratum and physical layersoftware and any associated hardware for communicating with the UMTSaccess network 1018. Similarly, the GSM access module 1014 includes theGSM access stratum and physical layer software and any associatedhardware for communicating with the GSM access network 1020. Inaddition, the UMTS and GSM access modules 1012, 1014 are operable toreceive handover requests from the UMTS and GSM access networks 1018,1020, and are also operable to initiate a handover request based onmeasurements taken of the UMTS and GSM access networks 1018, 1020, asdescribed in more detail below with reference to FIG. 7.

For example, if the device 1000 is communicating over the UMTS accessnetwork 1018, the UMTS access module 1012 may receive a handover requestto transfer the communication link from the UMTS access network 1018 tothe GSM access network 1020. In another example, while the device 1000is communicating over the UMTS access network 1018, the access modules1012, 1014 may monitor and measure the respective signal strengths ofthe access networks 1018, 1020. The UMTS access module 1012 may, forexample, monitor and measure adjacent GERAN cells and the GSM accessmodule 1014 may monitor and measure adjacent UTRAN cells. In addition,the UMTS and GSM access networks 1012, 1014 may each request cellmeasurements from the other access network 1020, 1018, as describedbelow with reference to FIG. 7. If the access network measurementsindicate that a less lossy communication link could be achieved over theGSM access network 1020, then the UMTS access module 1012 may initiate ahandover request. In addition, similar handover requests may be receivedor initiated by the GSM access module 1014 while the device 1000 iscommunicating over the GSM access network 1020.

The ASM module 1010 includes the access stratum manager software and anyassociated hardware for interfacing the UMTS access module 1012 and GSMaccess module 1014 with the NAS module 1008. The ASM module 1010 isoperable to establish a communication link between the NAS module 1008and the core network 1024 by activating either the UMTS access module1012 or the GSM access module 1014. In addition, the ASM module 1010 isfurther operable to maintain the communication link between the NASmodule 1008 and the core network 1024 while transferring thecommunication link between the UMTS and GSM access networks 1018, 1020in response to a handover request from the UMTS or GSM access modules1012, 1014. For example, if the UMTS access module 1012 has beenactivated by the ASM module 1010 to communicate over the UMTS accessnetwork 1018 and the ASM module 1010 receives a handover request, thenthe ASM module 1010 may activate the GSM access module 1014, transferthe communication link from the UMTS access module 1012 to the GSMaccess module 1014, and deactivate the UMTS access module 1012. Inaddition, the ASM module 1010 may perform similar functions to transfera communication link from the GSM access network 1020 to the UMTS accessnetwork 1018.

A further description of the operations of the dual mode protocol stackimplemented by the NAS module 1008, ASM module 1010, UMTS access module1012, and GSM access module 1014 is described below with reference toFIGS. 6-15.

FIG. 6 is a block diagram 1100 of an example dual-mode protocol stack1106 for a multi-mode mobile communication device. The dual-modeprotocol stack 1106 includes a non-access stratum 1108, an accessstratum manager 1110, a UMTS access stratum 1112, a GSM access stratum1114 and a physical layer 1116. Also illustrated are an IP application1102, a phone application 1103, and other device applications 1104 thatinterface with the dual-mode protocol stack 1106.

The non-access stratum 1108 (NAS) controls communications between thedevice applications 1102-1104 and a core network 1024. A more detaileddescription of the NAS 1108 is included in Standard document 3GPP TS24.008, which is incorporated herein by reference.

The UMTS access stratum 1112 controls communications over the UMTSaccess network 1018, and the GSM access stratum 1114 controlscommunications over the GSM access network 1020. In addition, the UMTSand GSM access strata 1112, 1114 are operable to receive handoverrequests from the UMTS and GSM access networks 1018, 1020, and toinitiate handovers based on the respective signal strengths of theaccess networks 1018, 1020, as described below with reference to FIG. 7.

The physical layer 1116 provides the physical interface(s) to the UMTSand GSM access networks 1018, 1020. The physical layer 1116 may includeportions specific to the protocols of the UMTS and GSM access networks1018, 1020, and may also include common portions used for connecting toeither access network 1018, 1020.

The access stratum manager 1110 interfaces the NAS 1108 with the UMTSand GSM access strata 1112, 1114. In operation, when the NAS 1108receives a command to establish a communication link between a deviceapplication 1102-1104 and a core network 1024, the access stratummanager 1110 activates one of the UMTS access stratum 1112 or GSM accessstratum 1114 to provide the air interface link over either the UMTS orGSM access network 1018, 1020. (See, e.g., FIGS. 11 and 12). Oncecommunications have been established, the active access stratum 1112 or1114 may request that communications be transferred to the non-activeaccess network 1112 or 1114 by sending a handover control signal 1120,1122 to the access stratum manager 1110. (See, e.g., FIG. 14). Uponreceiving a handover control signal 1120, 1122, the access stratummanager 1110 initiates a handover procedure between the UMTS and GSMaccess strata 1112, 1114. During the handover procedure, the accessstratum manager 1110 establishes a new connection between the targetaccess stratum 1112 or 1114 and the NAS 1108 and deactivates the oldconnection to the original access stratum 1112 or 1114. In addition, theaccess stratum manager 1110 also transmits a handover notificationsignal 1118 to the NAS 1108 which allows it to initiate an appropriatelocation updating procedure in the new access network. In this manner,communications may typically be transferred between the UMTS and GSMaccess networks 1018, 1020 without any appreciable loss in quality ofservice (QoS).

FIG. 7 is a more-detailed block diagram of the example dual-modeprotocol stack 1106 shown in FIG. 6 that illustrates examplesub-programs for initiating and controlling the handover procedurebetween the UMTS and GSM access networks 1018, 1020. The UMTS and GSMaccess strata 1112, 1114 each include a handover control sub-program1204, 1206, a cell reselection sub-program 1208, 1210, and a measurementcontrol sub-program 1212, 1214. The access stratum manager 1110 includesa handover notification sub-program 1202.

Within the UMTS and GSM access strata 1112, 1114, the measurementcontrol sub-programs 1212, 1214 communicate with the physical layer 1116to request signal strength measurements of adjacent cells belonging tothe UMTS and GSM access networks 1018, 1020. As illustrated, themeasurement control sub-program in each of the UMTS and GSM accessstrata 1212, 1214 may send both a GSM measurement request signal 1224and a UMTS measurement request signal 1226 to the physical layer 1116.That is, the active access stratum 1112 or 1114 may initiate signalstrength measurements of cells belonging to both access networks 1018,1020, while the inactive access stratum 1112 or 1114 remains idle. Inthis manner, both access networks 1018, 1020 may be actively measuredwhile conserving device resources. These measurement requests may beinitiated either by the cell reselection sub-programs, 1208, 1210 whenthe dual-mode protocol stack is responsible for cell-reselection or by asignal 1220, 1222 received from the currently active access network1018, 1020. The active measurement control subprogram returns themeasurement results to the originating source as appropriate.

The cell reselection sub-program 1208, 1210 in the active access stratum1112 or 1114 receives and compares the signal strength measurements ofcells in the UMTS and GSM access networks 1018, 1020 from the activemeasurement control sub-program 1212, 1214. The cell reselectionsub-program 1208, 1210 may, for example, include pre-determined signalstrength criteria that it used to determine when the device shouldinitiate a handover procedure. For example, if the measured signalstrength of the active access network falls below a pre-selected minimumthreshold level and the measured signal strength of the other accessnetwork is above a pre-selected threshold level, then the cellreselection sub-program may signal the active handover controlsub-program 1204, 1206 to request a handover.

The active handover control sub-program 1204 or 1206 receives internalhandover requests from the cell reselection sub-program 1208 based onsignal strength measurements taken by the mobile device, and may alsoreceive external handover requests 1216, 1218 from the current accessnetwork 1018 or 1020. In response to receiving a handover request fromthe cell reselection sub-program 1208, 1210 or from the access network1018, 1020, the handover control sub-program generates the handoverrequest signal to the access stratum manager 1110.

The access stratum manager 1110 initiates the handover procedure, asdescribed above, in response to the handover request signal from theactive handover control sub-program 1204, 1206. In addition, thehandover notification sub-program 1202 generates a handover notificationsignal to the NAS 1108 to inform the NAS 1108 of the handover from theold access stratum to the target access stratum. The handovernotification signal may include configuration details of the targetaccess stratum and network to identify any change in operationalparameters resultant from the handover.

FIGS. 8-15 are signal flow diagrams illustrating example operations of adual mode protocol stack 1106. FIGS. 8 and 9 are signal flow diagramsillustrating example signal routing in a dual mode protocol stack 1106during normal operation. FIG. 8 shows example signal routing for domainspecific signals (e.g., packet switched (PS) or circuit switched (CS)signals), and FIG. 9 shows example signal routing for signals that arenot domain specific.

With reference first to FIG. 8, three signals 1302, 1310, 1320 are shownbeing generated by the NAS 1108 and routed to the appropriate modulewithin the access strata 1112, 1114. A first domain-specific signal 1302is originated from a packet switched (PS) specific module within the NAS1108, such as a GMM (GPRS Mobility Management) module. When the accessstratum module 1110 receives the first domain-specific signal 1302, itdetects that the signal 1302 has originated from a packet switched (PS)specific module within the NAS 1108, and routes the new signal 1304 toeither a packet-switched specific module within the access strata suchas a GRR (GPRS Radio Resource control) module, or adds a parameter tothe signal indicating it belongs to the PS domain and routes the newsignal 1306, to a non-domain-specific module within the access strata1112, 1114, such as a RRC (Radio Resource Control) module or possibly aRR ([GSM] Radio Resource) module (a RR module may be domain specific ornon-domain specific).

A second domain-specific signal 1310 is originated from a circuitswitched (CS) specific module within the NAS 1108, such as a MM(Mobility Management) module. When the access stratum module 1110receives the second domain-specific signal 1310, it detects that thesignal 1310 has originated from a circuit switched (CS) specific modulewithin the NAS 1108, and routes the new signal 1312 to either acircuit-switched module such as a RR module within the GSM accessstratum, 1114, or adds a parameter indicating the signal belongs to theCS domain and sends this new signal, 1314, to a non-domain-specificmodule within the access strata 1112, 1114, such as a RRC module orpossibly a RR module.

A third domain-specific signal 1320 is originated from a module (OTHER)within the NAS 1108 that is not itself domain specific. In this case,the NAS 1108 adds a domain-specific parameter to the signal 1320 thatindicates the proper domain (e.g., PS or CS). When the signal 1320 isreceived by the access stratum manager 1110, the domain-specificparameter is detected by the access stratum manager 1110. At this point,three alternatives are illustrated. First, a new signal, 1322, strippedof its PS domain-specific parameter may be sent to a PS domain-specificmodule of the access stratum, for example, the GRR of the GSM accessstratum, 1114. Second, a new signal, 1324, stripped of its CSdomain-specific parameter may be sent to a CS domain-specific module ofthe access stratum, for example, the RR of the GSM access stratum, 1114.Third, the signal, 1326, still containing its domain-specific parameter,may be passed to a non-domain-specific module of the access stratum,such as the RRC of the UMTS access stratum, 1112.

With reference now to FIG. 9, an indication signal 1410 and a requestsignal 1452 are shown being generated by the NAS 1108 and routed to theappropriate access stratum 1112 or 1114. When generated by the NAS 1108,the indication signal 1410 and request signal 1452 are generic in thesense that they are not formatted for a particular access network. Uponreceiving the generic signal 1410, 1452 from the NAS 1108, the accessstratum manager 1110 formats the signal 1410, 1452 based on which of theaccess stratum 1112, 1114 is currently active, and forwards theformatted signal 1412, 1414, 1454, 1458 to the active access stratum1112 or 1114. In the case of a request signal 1454, 1458, the activeaccess stratum 1112 or 1114 returns a confirm signal 1456, 1460 to theaccess stratum manager 1110. The access stratum manager 1110 thenreformats the received confirm signal 1456 or 1460 into a genericconfirm signal 1462 and routes the generic signal 1462 to the NAS 1108.

FIG. 10 is a signal flow diagram 1500 illustrating example signalrouting within the dual mode protocol stack 1106 when the device isinitialized (e.g., at start-up). The initialization sequence 1500 beginswith the access stratum manager 1100 generating stack request signals1535, 1540 for initializing the UMTS access stratum 1112 and the GSMaccess stratum 1114, respectively. The access stratum manager 1110 thenwaits for stack confirmation signals 1550, 1555 from the access stratum1112, 1114 for a pre-defined period of time 1545.

Within the NAS 1108, there are various NAS sub-modules that may have tocommunicate directly with the access strata 1112, 1114. Theseidentifiers 1575 are communicated to the access stratum manager 1110,which forwards the identifiers 1580, 1585 to the access strata 1112,1114 to complete the initialization sequence 1500.

FIG. 11 is a signal flow diagram 1600 illustrating example signalrouting within the dual mode protocol stack 1106 to select a public landmobile network (PLMN). This sequence may, for example, be initiatedfollowing the initialization sequence shown in FIG. 10. The NAS 1108determines a priority order for the available PLMNs and their respectiveradio access technologies (RATs), in accordance with the 3GPP standards.(See, e.g., Standard Document TS 23.122). Based on this determination,the NAS 1108 instructs the access stratum manager 1110 to select thehighest priority PLMN/RAT by generating a RAT PLMN search request signal1640. The RAT PLMN search request signal 1640 may, for example, includea mode parameter, a PLMN identification, a RAT type indicator, and alist of any equivalent PLMNs. The mode parameter may, for example,control details of the PLMN selection operation, such as instructing theaccess stratum manager 1110 to perform a full initial search, use storeddetails to speed up the search, search for any acceptable cell, or otherinstructions.

Upon receiving the RAT PLMN search request 1640, the access stratummanager 1110 activates 1700 the access stratum 1112 or 1114 associatedwith the selected PLMN (see FIG. 12), and generates a PLMN searchrequest signal 1650U or 1650G to the activated access stratum 1112 or1114. The PLMN search request 1650U or 1650G identifies the selectedPLMN, and may include the mode parameter, the list of equivalent PLMNs,or other relevant information. The activated access stratum 1112 or 1114then scans the air interface for the selected PLMN.

If the selected PLMN is located by the active access stratum 1112 or1114, then the access stratum camps on the strongest cell in that PLMNand returns a PLMN select confirm signal 1660U or 1660G to the accessstratum manager 1110. The PLMN select confirm 1660U or 1660G may, forexample, indicate that the selected PLMN was successfully contacted, andmay also include a PLMN identification. In response, the access stratummanger 1110 generates a PLMN search confirm signal 1680 to the NAS 1108.The PLMN search confirm signal 1680 may, for example, include a successcode, the PLMN identification and a RAT type identification

If the selected PLMN is not located by the active access stratum 1112 or1114, then the selected access stratum may return a failure code andidentify any PLMNs that were located. If a GSM PLMN was searched for,then the failure code and list of located PLMNs may be returned to theaccess stratum manager 1110 in a PLMN select signal 1660G from the GSMaccess stratum 1114. If a UMTS PLMN was searched for, however, then theUMTS access stratum 1112 generates a PLMN list confirmation signal thatincludes the failure code and identifies the located PLMNs. In addition,upon failing to locate the selected PLMN, the active access stratum 1112or 1114 may camp on one of the located PLMNs to enable emergency calls.The access stratum manager 1100 may then generate a RAT PLMN signal 1690to the NAS 1108 that includes the list of located PLMNs and the failurecode. The NAS 1108 may then determine the next highest priority PLMN/RATand repeat the PLMN selection sequence 1600. In addition, if the homePLMN of the device is not located, then the sequence 1600 may berepeated at pre-selected time intervals to search for a better PLMN, asdetailed in the 3GPP Standard Document TS23.122.

FIG. 12 is a signal flow diagram illustrating example signal routingwithin the dual mode protocol stack 1106 to activate an access stratum1112, 1114. This activation sequence 1700 may, for example, be initiatedby the PLMN selection procedure 1600 shown in FIG. 11. The sequence 1700begins with an activate signal 1750 or 1755 specific to the selectedaccess stratum 1112 or 1114 being generated by the access stratummanager 1110. Upon receiving the activate signal 1750 or 1755, theselected access stratum 1112 or 1114 may require data located in thedevice USIM (for UMTS) or SIM (for GSM) and sends a request for thenecessary USIM access 1760 or SIM access 1765 parameters to the accessstratum manager 1110.

The access stratum manager 1110 converts the request 1760 or 1765 fromthe access stratum 1112 or 1114 into a generic SIM request 1770 that isforwarded to the NAS 1108. The NAS 1108 then extracts the required USIMor SIM parameters, and returns the information to the access stratummanager 1110 in a SIM confirm signal 1780. The access stratum manager1110 forwards the data to the selected access stratum 1112 or 1114 in aUSIM or SIM data signal 1790 or 1795. Upon receiving the USIM or SIMdata signal 1790 or 1795, the selected access stratum 1112 or 1114 isable to complete its activation and returns an activate confirmationsignal 1796 or 1798 to the access stratum manager 1110.

FIG. 13 is a signal flow diagram 1800 illustrating example signalrouting within the dual mode protocol stack 1106 to implement a networkinitiated handover sequence. The handover sequence 1800 begins when acell change order or a handover command 1216, 1218 (see FIG. 7) isreceived from the access network by the active access stratum 1112 or1114. Note this could be either a handover command or a cell changeorder. The active access stratum 1112 or 1114 validates the handovercommand 1216, 1218 and extracts any encoded information necessary toimplement the handover (i.e. intended for the target access stratum) andincludes the encoded handover information in a handover request signal1840 to the access stratum manager 1110.

Upon receiving the handover request 1840, the access stratum manager1110 partially activates (if necessary to bring it to a state where itcan respond to the handover request) the target access stratum 1112 or1114, and passes the encoded handover information to the target accessstratum 1112 or 1114 in a handover configuration request signal 1860.The handover configuration request 1860 includes the encoded informationnecessary to configure the target access stratum 1112 or 1114 forcommunication with the desired network. It may also include a list ofequivalent PLMNs. The target access stratum 1112 or 1114 then configuresitself by decoding and processing the configuration information includedin the handover configuration request 1860, and may also pre-configurethe physical layer in preparation for activation with the new network.If the configuration is successful, then the target access stratum 1112or 1114 returns a handover configuration confirmation signal 1870 to theaccess stratum manager 1110 indicating that the target access stratum1112 or 1114 is ready to take control of network communication.Otherwise, if the configuration is invalid or unsupported by the targetaccess stratum 1112 or 1114, then the handover configuration confirmsignal 1870 is returned with a failure status message and an appropriateerror code.

If the handover configuration signal 1870 indicates that theconfiguration is invalid or unsupported, then the handover sequence 1800is aborted and the error code and failure message are returned to thecore network. Otherwise, if the handover configuration confirmationsignal 1870 indicates that the target access stratum 1112 or 1114 isready to take over network communication, then a handover confirmationsignal is sent from the access stratum manager 1110 to the active accessstratum 1112 or 1114 indicating that the target access stratum 1112 or1114 is configured. The active access stratum 1112 or 1114 may thenhandover either immediately, or may defer handover for a pre-determinedtime period to synchronize with changes at the network. If handover isimmediate, then the active access stratum 1112 or 1114 may releasecontrol of the physical layer but without, at this point, releasingcontrol of its other internal resources (i.e. those in layer two and theNAS 1108). If handover is deferred, then the active access stratum 1112or 1114 waits for the specified time period and then releases control ofthe physical layer. In either case, once the physical layer is released,the active access stratum 1112 or 1114 sends a handover indicationsignal 1882 to the access stratum manager 1110.

Upon receiving the handover indication signal 1882, the access stratummanager 1110 sends a complete handover request signal 1884 to the targetaccess stratum 1112 or 1114 indicating that the target access stratum1112 or 1114 may take control of network communication. The targetaccess stratum 1112 or 1114 then completes its physical layerconfiguration and attempts to select the cell specified in the handoverconfiguration 1860 and establish a signaling connection to the corenetwork. If the target access stratum 1112 or 1114 establishes asuccessful connection to the core network, then a complete handoverconfirmation signal 1886 is returned to the access stratum managerindicating that the handover operation was successful. If the connectionto the core network is unsuccessful, however, then the target accessstratum 1112 or 1114 switches control of the physical layer back to theactive access stratum 1112 or 1114, frees its internal resources, andreturns the complete handover confirmation signal with an error code.

Upon receiving a complete handover confirmation signal 1886 indicating asuccessful handover, the access stratum manager 1110 generates ahandover notification signal 1888 to the NAS 1108 indicating that asuccessful handover has been completed and signaling the NAS 1108 toinitiate any appropriate location updating procedures. In addition, upona successful handover, the access stratum manager 1110 generates ahandover response signal 1890 to the originally active access stratum1112 or 1114 indicating a successful handover. The originally activeaccess stratum 1112 or 1114 may then free all its internal and any NASresources.

If the complete handover confirmation signal 1886 indicates that thetarget access stratum 1112 or 1114 could not connect to the corenetwork, then the access control manager 1110 forwards the error codeinformation to the originally active access stratum 1112 or 1114 in ahandover response signal 1890. The originally active access stratum 1112or 1114 then reconnects to the physical layer and sends a handoverfailure message to the core network.

In addition, the originally active access stratum 1112 or 1114 may starta timer upon sending the handover indication signal 1882 to the accessstratum manager 1110. If the handover response signal 1890 is notreturned before the timer expires, then the originally active accessstratum 1112 or 1114 may send a handover abort signal to the accessstratum manager 1110, instructing the access stratum manager 1110 todeactivate the target access stratum 1112 or 1114. The access stratummanager 1110 may then return a handover abort confirm signal to theoriginally active access stratum 1112 or 1114, which retakes control ofthe physical layer and restores its previous configuration. A handoverfailure message may then be transmitted from the reactivated accessstratum 1112 or 1114 to the core network.

FIG. 14 is a signal flow diagram illustrating example signal routingwithin the dual mode protocol stack 1106 to implement an internallyinitiated handover sequence 1900. The handover sequence 1900 may, forexample, be initiated by an inter-RAT cell reselection event. Thehandover sequence 1900 begins with a cell reselect request 1940generated by the active access stratum 1112 or 1114 in response tosystem information broadcast from the current cell and from the measuredsignal strengths of the current and neighboring cells, as describedabove with reference to FIG. 7. That is, the active access stratum 1112or 1114 may continually monitor for a better cell, and may generate theinter-RAT cell reselect request if it locates a better cell in theinactive (target) access network 1112 or 1114.

The cell reselect request 1940 is received by the access stratum manager1110, which responds by generating a partial deactivation signal 1950 tothe active access stratum 1112 or 1114 instructing the active accessstratum 1112 or 1114 to release control of the physical layer. Theaccess stratum manager 1110 then activates the target access stratum1112 or 1114 (as described in FIG. 12) and sends a PLMN select requestsignal 1970. The PLMN select request signal 1970 includes the ‘better’cell details and a mode parameter to ensure that the target accessstratum 1112 or 1114 selects that cell and no other. Upon receiving thePLMN select request 1970, the target access stratum 1112 or 1114 locatesand camps on the specified cell and returns a PLMN select confirmationsignal 1980 to the access stratum manager 1110 indicating a successfulconnection. If the target access stratum 1112 or 1114 does notsuccessfully locate and connect to the desired cell, then an error codeis returned in the PLMN select confirmation signal 1980 to the accessstratum manager 1110.

If the PLMN select confirmation 1980 indicates a successful connection,then the access stratum manager 1110 generates a handover notificationsignal 1985 to the NAS 1108 that indicates that a new PLMN has beenselected, and also identifies the selected PLMN and RAT type. Inaddition, the access stratum manager 1110 sends a cell reselectionconfirm 1950 to the originally active access stratum 1112 or 1114 thatinstructs the access stratum to free up all of its resources and enteran inactive state. The NAS 1108 then generates a location updatingrequest 1995 to the access stratum manager 1110, which sends acorresponding signal 1997 to the target access stratum 1112 or 1114 toestablish a signaling connection to initiate a location updatingprocedure.

If the PLMN select confirmation signal 1980 from the target accessstratum 1112 or 1114 indicates a failed attempt to establish a networkconnection, then the access stratum manager 1110 sends a deactivatecommand to the target access stratum 1112 or 1114. The access stratummanager 1110 then sends a cell reselection confirm signal 1950 to theoriginally active access stratum 1112 or 1114 with a failure code. Inresponse to the failure code, the originally active access stratum 1112or 1114 may retake control of the physical layer and attempt toreconnect to a cell in the original RAT.

FIG. 15 is a signal flow diagram illustrating example signal routingwithin the dual mode protocol stack 1106 for handling UMTS systeminformation blocks (SIB) while in GSM mode. When the dual-mode device isin GSM mode (e.g., the GSM access stratum 1114 is active), the devicemay be required by the network specifications to receive and respond toinformation that is broadcast from UMTS cells, such as pre-defined UTMSconfiguration details (e.g., SIB16). When the active GSM access stratum1114 receives a SIB16 broadcast including UMTS pre-defined configurationinformation, then the encoded UMTS configuration information isforwarded to the access stratum manager 1110 in a UMTS systeminformation indication signal 2012. The access stratum manager 1110 thenreformats the encoded UMTS configuration information into a RRC systeminformation indication signal 2010 and routes the signal 2010 to theUMTS access stratum 1112 for processing. Upon receiving the RRC systeminformation indication signal 2010, the UMTS access stratum 1112 decodesthe pre-defined UMTS configuration information and stores the decodedconfiguration details in a memory location.

After the predefined UMTS configuration details have been decoded andstored by the UMTS access stratum 1112, the GSM access stratum 1114 mayquery the access stratum manager 1110 with a predefined configurationidentification request 2022. The request signal 2022 is then reformattedby the access stratum manager 1110 into an RRC predefined configurationrequest signal 2020 and routed to the UMTS access stratum manager 1112.Upon receiving the request signal 2020, the UMTS access stratum 1112 maycreate a list of the stored predefined configurations and return thelist in a RRC predefined configuration confirm signal 2026 to the accessstratum manager 1110. The configuration confirm signal 2026 isreformatted for the GSM access stratum 2028 and routed from the accessstratum manager 1110 to the GSM access stratum 1114.

Also illustrated in FIG. 15 is an RRC predefined configuration deletesignal 2030 that may be generated by the access stratum manager 1110 tocause the UMTS access stratum to delete 2032 the predefined UMTSconfigurations from memory.

This written description uses examples to disclose the invention,including the best mode, and also to enable a person skilled in the artto make and use the invention. The patentable scope of the invention mayinclude other examples that occur to those skilled in the art. Forexample, in other embodiments, the multi-mode mobile communicationdevice may be operable to communicate over and transfer communicationsbetween wireless access networks other than the UMTS and GSM accessnetwork.

1. A multi-mode mobile communication device for use in a plurality ofwireless access networks, the multi-mode mobile communication devicebeing operable to establish a communication link with a core networkover a first wireless access network and transfer the communication linkfrom the first wireless access network to a second wireless accessnetwork, comprising: a first access module operable to communicate overthe first wireless access network; a second access module operable tocommunicate over the second wireless access network; a non-accessstratum (NAS) module operable to communicate using a protocol compatiblewith the core network; an access stratum manager (ASM) module thatinterfaces the NAS module with the first and second access modules; theASM module being operable to establish the communication link betweenthe NAS module and the core network using the first access module; andthe ASM module being further operable to maintain the communication linkbetween the NAS module and the core network while transferring thecommunication link from the first access module to the second accessmodule; wherein the multi-mode mobile communication device measures therespective signal strengths of the first wireless access network and thesecond wireless access network, and the ASM module initiates thetransfer of the communication link from the first access module to thesecond access module in response to a handover control signal generatedby first access module in response to the measured signal strengths. 2.The multi-mode mobile communication device of claim 1, wherein the ASMmodule sends a handover notification signal to the NAS module thatindicates that the communication link is being transferred from thefirst wireless access network to the second wireless access network. 3.The multi-mode mobile communication device of claim 2, wherein inresponse to receiving the handover notification signal, the NASgenerates a location updating request signal that causes the secondaccess module to initiate a location updating procedure.
 4. Themulti-mode mobile communication device of claim 1, wherein one of thefirst wireless access network or the second wireless access network is aUniversal Mobile Telecommunications System (UMTS).
 5. The multi-modemobile communication device of claim 1, wherein one of the firstwireless access network or the second wireless access network is aGlobal System for Mobile Communications (GSM) network.
 6. The multi-modemobile communication device of claim 1, wherein the NAS moduleinterfaces a device application with the core network.
 7. The multi-modemobile communication device of claim 6, wherein the device applicationis an internet protocol (IP) application.
 8. The multi-mode mobilecommunication device of claim 7, wherein the IP application is anelectronic mail application.
 9. The multi-mode mobile communicationdevice of claim 7, wherein the IP application is a web browserapplication.
 10. The multi-mode mobile communication device of claim 6,wherein the device application is a telephony application.
 11. Themulti-mode mobile communication device of claim 1, wherein the firstaccess module initiates the signal strength measurements of both thefirst wireless access network and the second wireless access network.12. The multi-mode mobile communication device of claim 11, wherein thesecond access module remains in an inactive state while multi-modemobile communication device measures the signal strengths of the firstand second wireless access networks.
 13. In a multi-mode mobilecommunication device including a processing device, a memory sub-system,a communication sub-system operable to communicate with a plurality ofwireless access networks, and a protocol stack stored in the memorysub-system and executed by the processing device, the protocol stackcomprising: a first access stratum for communicating with a firstwireless access network via the communication sub-system; a secondaccess stratum for communicating with a second wireless access networkvia the communication sub-system; a non-access stratum (NAS) forcommunicating with a core network; an access stratum manager forinterfacing the NAS with the first and second access strata; the accessstratum manager being operable to activate the first access stratum toestablish a communication link with the core network over the firstwireless access network; and the access stratum manager being furtheroperable to maintain the communication link between the NAS and the corenetwork while transferring the communication link from the first accessstratum to the second access stratum; wherein the multi-mode mobilecommunication device measures the respective signal strengths of thefirst wireless access network and the second wireless access network,and the access stratum manager initiates the transfer of thecommunication link from the first access stratum to the second accessstratum in response to a handover control signal generated by the firstaccess stratum in response to the measured signal strengths.
 14. Theprotocol stack of claim 13, wherein the multi-mode mobile communicationdevice further includes a software application stored in the memorysub-system and executable by the processing device, the softwareapplication when executed by the processing device being operable usethe non-access stratum to communicate with the core network.
 15. Theprotocol stack of claim 13, wherein the access stratum manager sends ahandover notification signal to the NAS that indicates that thecommunication link is being transferred from the first wireless accessnetwork to the second wireless access network.
 16. The protocol stack ofclaim 13, wherein the first wireless access network or the secondwireless access network is a Universal Mobile Telecommunications System(UMTS) network.
 17. The protocol stack of claim 13, wherein the firstwireless access network or the second wireless access network is aGlobal System for Mobile Communications (GSM) network.
 18. The protocolstack of claim 13, wherein the first access stratum includes ameasurement control sub-program that communicates with a physical layerto request the signal strength measurements for the first wirelessaccess network and the second wireless access network.
 19. The protocolstack of claim 18, wherein the first access stratum further includes acell reselection sub-program that receives the signal strengthmeasurements from the measurement control sub-program and compares thesignal strength measurements, wherein the handover control signal isgenerated based on the comparison of the signal strength measurements.20. The protocol stack of claim 19, wherein the first access stratumfurther includes a handover control sub-program that receives a handoverrequest signal from the cell reselection sub-program based on thecomparison of the signal strength measurements and, in response to thehandover request signal, generates the handover control signalinstructing the access stratum manager to initiate the transfer of thecommunication link from the first access stratum to the second accessstratum.
 21. The protocol stack of claim 13, wherein the multi-modemobile communication device may also initiate the transfer of thecommunication link from the first access stratum to the second accessstratum in response to a handover request signal received from the firstwireless access network.
 22. The protocol stack of claim 21, wherein thefirst wireless access network receives the signal strength measurementsof the first wireless access network and the second wireless accessnetwork from the multi-mode mobile communication device and generatesthe handover request signal based on the received signal strengthmeasurements.
 23. The protocol stack of claim 13, wherein in response tothe access stratum manager initiating the transfer of the communicationlink from the first access stratum to the second access stratum, thefirst access stratum enters a partially active state until thecommunication link is successfully established with the second accessstratum.
 24. The protocol stack of claim 23, wherein if thecommunication link is successfully established with the second accessstratum, then the first access stratum enters an inactive state.
 25. Theprotocol stack of claim 23, wherein if the communication link is notsuccessfully established with the second access stratum, then the firstaccess stratum returns to an active state and the second access stratumenters an inactive state.